This invention relates to a control valve such as a subsea test tree for use in a submerged oil well, said test tree control valve adapted to be positioned within a subsea blowout preventer stack for controlling the flow of fluids through a testing string located in an offshore oil well during a production test or the like.
During the testing of offshore wells it is desirable to include in the testing string a control valve which is positioned in the vicinity of a blowout preventer stack. This blowout preventer stack normally rests on the sea floor with the control valve located in the stack for controlling oil well fluids through the testing string.
These test tree control valves are preferably operated using hydraulic pressure to actuate tandem valves for opening and closing the flow path through the valve apparatus. It has been the practice in the past to include hydraulic lines lowered from the surface of the sea to supply operating hydraulic fluid to control the tandem valves. For instance, such control valves have been disclosed in U.S. Reissue Pat. No. Re. 27,464 to Taylor reissued Aug. 22, 1972 and U.S. Pat. No. 3,967,647 to Young issued July 6, 1976. These control devices may include separate hydraulic fluid control lines, or concentric tubing strings extending from the control device to the surface.
Separate hydraulic fluid supply lines may be caught on obstructions beneath the surface of the water and are particularly troublesome when the testing string must be rotated to set the packer mechanism at the lower end of the testing string. In this case, the hydraulic fluid control lines wrap around the testing string extending from the control apparatus to the surface of the ocean.
Concentric tubing strings are also difficult to handle and to assemble as the testing string is lowered into the well.
The present invention provides a subsea oil well testing control valve wherein hydraulic fluid is provided by pressuring the well annulus below closed blowout preventer rams. The supplying of hydraulic pressure to operate the test tree valve in this manner eliminates separate hydraulic control lines or devices such as concentric tubing strings. A control line is used which is presently in place and available and which does not need to be rotated as the packer mechanism at the lower end of the testing string is set. The apparatus of the present invention includes tandem bal valves which are moved to the open position by hydraulic pressure supplied to the well annulus below a closed set of blowout preventer rams.
A separate fluid passageway is provided through the tool to provide operating control pressure transmitted to the tandem ball valves from the well annulus below a closed set of blowout preventer rams. A separate exhaust passageway is provided for setting a reference pressure in the subsea control apparatus and for exhausting hydraulic fluid to a position above the closed blowout preventer rams for allowing operation of the tandem ball valves. A quick release mechanism is also provided which allows for quickly releasing the testing string conduit above the control valve apparatus by applying well annulus pressure to below a separate set of closed blowout preventer rams. The quick release mechanism may also be operated by lifting the testing string from the surface and unscrewing from the test tree the conduit which extends from the control valve to the surface.
Release of well annulus pressure causes the tandem ball valves to reclose by spring actuating forces. The tandem ball valves are arranged such that the valves are operated independently. Thus, if one valve is prevented from closing, the second valve shall continue to close under operation of an independent ball closing mechanism.
A hydraulic reservoir section is present in the apparatus such that hydraulic fluid supplied to the tandem ball valves may be isolated from fluid appearing in the well annulus. Thus, the tandem ball valves are operated by a clean hydraulic fluid which is not contaminated by well annulus fluid.
The blowout preventer stack may vary in design and spacing from well to well. For this reason, means are provided in the invention for varying the control passageway access spacing to match the spacing of the rams used in conjunction with the control valve apparatus.
The tandem ball valves of the invention disclosed may be moved to the open position by applying fluid pressure to the well annulus below the closed rams of the blowout preventer stack, and then subsequently closing a second set of blowout preventer rams in the preventer stack thereby trapping an operating pressure between the two sets of blowout preventer rams.
The apparatus of the present invention is particularly advantageous when run with the well testing apparatus operated by well annulus pressure. Thus, once the packer is set the entire testing operation may be controlled by applying pressure to the well annulus. A first set of blowout preventer rams is closed and well annulus pressure is supplied to open the tandem ball valves in the disclosed invention. A second lower set of blowout preventer rams is closed to entrap the ball valve opening pressure between the two sets of closed rams. Additional well annulus pressure may then be applied to operate an annulus pressure responsive tester valve in the lower portion of the well string or an annulus pressure responsive circulation valve when desired.
To quickly release the testing string above the control apparatus it is only necessary to open the lower two sets of blowout preventer rams and to close a higher third set of blowout preventer rams while applying hydraulic pressure to the well annulus. Well annulus pressure trapped below the topmost blowout preventer rams move the quick release section to the open condition allowing the testing string above the control device to be quickly and easily withdrawn from the invention.